LOL antonius I feel VERY sorry for u now! U didn't need to look at every spell file to see which one it is. All the spell codes are listed in the language.txt file which is in the BG2 main directory.
The 'possibilities' for the CLAB*.2da files are endless. Just use the name of the .SPL file after the standard AP_ or GA_. I assume u know this already though.
I am afraid it is no go with the casting spells from scrolls ability, unless u wanna edit every scroll as someone already mentioned. Some things are hard-coded into the game's exe which means we cannot get at them (until someone works out how to upack then repack it- not likely
), and I think giving non spellcasters spellbooks is like this as well so u can't give a thief kit a spellbook.
There is also a nice new utility called Near Infinity which is helpful for general editing but it is quite similar to IE. It should be linked from teambg.